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arXiv · 2508.01900

Lattice Calculation of Short-Range Contributions to Neutrinoless Double-Beta Decay $\pi^-\to\pi^+ ee$ at Physical Pion Mass

Peter Boyle·Felix Erben·Xu Feng·Jonathan M. Flynn·Nicolas Garron·Taku Izubuchi·Luchang Jin·Rajnandini Mukherjee·J. Tobias Tsang·Xin-Yu Tuo
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Abstract

Neutrinoless double-beta ($0\nu\beta\beta$) decays provide an excellent probe for determining whether neutrinos are Dirac or Majorana fermions. The short-range matrix elements associated with the $\pi^- \to \pi^+ ee$ process contribute at leading order in the $0\nu\beta\beta$ decay channel $nn \to ppee$ through pion exchange between nucleons. However, current lattice calculations show notable discrepancies in predicting these short-range contributions. To address this issue, we perform a lattice QCD calculation of the $\pi^- \to \pi^+ ee$ matrix elements using domain wall fermion ensembles at the physical pion mass generated by the RBC and UKQCD Collaborations. To mitigate contamination from around-the-world effects, we develop a new method to reconstruct and subtract them directly from lattice data. We then perform a nonperturbative renormalization using the RI/SMOM scheme. Compared with previous studies, this work reduces the uncertainties in the matrix elements and provides an independent cross-check that helps to reconcile the discrepancies among previous lattice calculations.

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Peter Boyle, Felix Erben, Xu Feng, Jonathan M. Flynn, Nicolas Garron, Taku Izubuchi, Luchang Jin, Rajnandini Mukherjee, J. Tobias Tsang, Xin-Yu Tuo. 2025-08-03. Lattice Calculation of Short-Range Contributions to Neutrinoless Double-Beta Decay $\pi^-\to\pi^+ ee$ at Physical Pion Mass. https://arxiv.org/abs/2508.01900

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